1. Technical Field
The present invention relates to a method and apparatus for driving and controlling a plurality of electrical on-vehicle loads, and in particular to the method and apparatus that distributes electric power generated by an on-vehicle generator to the loads using pluralities given to the loads in advance.
2. Related Art
In recent years, the types of electrical loads (hereinafter, simply referred to as loads) mounted on vehicles, such as automobiles, and the total power consumption has been increased remarkably. It is supposed that this tendency will continue.
In addition, there is a tendency of employing a load drive system configured only by an electrical system without using mechanical components, as provided by a steer-by-wire system, which connects an operation device and an actuator. Such load drive system is very significant in that the system is directly concerned with some fundamental functions of the vehicle. Thus, the significance of stable supply of the power to the loads is growing.
When considering the current situations, however, problems attributable to vehicle mounting performance and manufacturing cost pose a limitation to an amount of power available from the power supplies, such as on-vehicle generator and batteries. Therefore, there is a possibility that a peak of power consumption that lasts only a short period of time exceeds temporarily a maximum capacity of the on-vehicle power equipment. This often results in a temporally shortage of power to be supplied to the loads, which may spoil comfortable driving conditions. Therefore, it has been desired to have a countermeasure against such a shortage in the power supply such that the power is supplied to significant electrical loads in charge of the fundamental functions of a vehicle (high-priority loads) in preference to other loads.
One of such countermeasures is provided by Japanese Patent Laid-open (KOKAI) publication No. 9-190055. This publication provides a technique that, when a sum of rated power of load in operation exceeds a predetermined allowable capacity, information about priorities previously given to the loads is read out. And based on the priorities, loads of which priories are lower are in turn subjected to a reduction in an amount of the supplied power or a shutdown of the power. Thus, the significant loads are given priority over the other loads.
However, the foregoing power-distributing technique proposed by the publication reference uses previously fixed priorities of loads. Thus, once a shortage of the power to be supplied is caused, loads given to lower priorities are obliged to have a lowered operation level or to accept the complete shutdown until the power supply is restored up to a sufficient level. Such a condition results in largely degraded amenity for crews.
In addition, a recent trend that the number of on-vehicle loads increases has been remarkable, with the result that the conventional technique of centrally controlling the priorities of loads is confronted with a difficulty. In other words, the number of on-vehicle loads and the capacities thereof should be changed due to for example vehicles' model changes. Whenever such an occasion arises, it should be necessary to re-adjust the priority order of the loads, thus resulting in an increased number of steps of development.